1. Field of the Invention
The present invention relates to a hand screw driver, and more particularly to a hand screw driver employing an offset shank rotating with respect to a handle, thereby carrying out a desired screw driving function without the necessity of providing an intermission for releasing the twisted state of the user's wrist during the screw driving operation.
2. Description of the Prior Art
Screw drivers are generally classified into plus driver and minus-type drivers in accordance with the shape of a screwdriver's recessed tip. Another type of driver having a recessed tip, for example, a tip having a square cross section or a tip having a hexagonal cross section, has been proposed and widely used. As well known to those skilled in the art, the plus driver and the minus driver are used for tightening or releasing plus-type bolts and minus-type bolts, respectively. A fixed type screw driver, which is most wide used, is restricted in its use since its shank having the tip is fixed to the handle.
In addition, when a high screw driving force is required, a motor screw driver or a torque control driver is preferably used. On the other hand, there has been proposed an offset screw driver which is provided with a crank-shaped shank suitable for increasing the torque imparted to the screw.
In operation of the fixed type screw driver, the tip of the shank is placed on the recessed head of a screw and the handle fixed to the shank is rotated to impart the rotational force or the driving force to the screw. In order to rotate the handle of the fixed type screw driver, the user's wrist is inevitably twisted, so that it should be required to often intermit the screw driving work in order to release the twisted state of the wrist and regrip the handle. Thus, the known fixed type screw driver has a problem in that the screw driving work using it is regarded as a burdensome work.
When using the known offset screw driver, the intermission of the screw driving work caused by the twisted state of the user's wrist is overcome. However, the known offset screw driver has a problem in that it is relatively complicated in its construction and involves capital investment. Furthermore, the handles of the known offset screw driver are rotatably mounted on the offset shank, respectively, so that it is difficult to place the tip of the shank on the recessed head of a screw to be tightened or released.